Telephone system



TELEPHONE SYSTEM Fild June 17, 193e l 6 Sheets-Sheet l NSN June 6,` 1939. R. E. coLLIs ET AL TELEPHONE SYSTEM Fiigd June 17, 1958 e sheets-sheet 2 kvm /NVEA/ro/Ps; P- E COLL/S v l, I n

J 5 NEWSOM www W a( ATT' NEV June 6, 1939. R. E. coLLls ET AL TELEPHONE SYSTEM Filed June 17, '1938 e sheets-sheet s June 6, 1939. R. E. coLLls Er AL 2,161,456

' TELEPHONE SYSTEM Filed June 17, 1958 6 Sheets-Sheet 4 R. E. COLL/s J. 5. Nen/50M um ATTO EV I.: z 2 .l s 3 m. .bfi

June 6, 1939.

R. E. coLLls ET AL 2,161,456

TELEPHONE SYSTEM Filed June 17, 1958 6 Sheets-Sheet' SECONDARY T0 MA TE OFF/CE FRAME OFF/CE S R. E. COLL/SI /NVENTORSJ B NEWSOM BV STTORV June 6, 1939.

PLRIZED R. E. COLLIS ET AL TELEPHONE SYSTEM Filed June 17, 1958 6 Sheets-Shes?l 6 ATTO/Q EV Patented June 6, 1939 PATENT OFFICE TELEPHONE SYSTEM Raymond E. Collis, Summit, N. J., and James B. Newsom, Great Neck, N. Y., assignors to YBell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New -York Application June 17,

5 Claims.

This invention relates totelephonesystems and particularly lto vthose .employing `automatic switching'equipment for establishing connections.

f "The ,objects of the invention are to improve the 4 testing-mechanisms used to select trunks or other conversational circuits; to safeguard these circuits against the .possibility of being selected simultaneously for Vmore than one conversational connection; and tofeifect other improvements in .systems of this kind.

:Large .central .,oice systems have-been proposed o lheretofore in which telephone connections are establishedfrom subscribers lines to trunks by :means of switchesY ofthe cross-bar type under the :control of i. central .oiice register senders and markers. The markersare common to the frames of switches on which the groups of outgoing r:trunks appear, and connecting means is provided for, associating a marker having the registered `.information `concerning a call with .the ,switch -Irame having access to therdesired group of trunks. The rmarker, when associated with the desired v .trunklgroun makes a test of them and selects .an idle one for use. VThe association of a marker f withthe switch frame/for rvthe purpose of testing aigroup of trunkszlasts only for 4a brief interval .,ofV 1time,fand duringthis periodother markersare =excluded from .that particular frame. In some ,-,cases, however, :where two centraloice units are ,located lin the same building for vin .close relation to :each other itis desirable that both central .oiiiceunits have access to the same group of out- .fgoingitrunks VAlthough the Imarkersof the same .central ofiice unit exclude each other automatic- .f .ally from a connection .to any one of the frames `in that central office unit, the markers of one central voffice are entirely independent of those ofithe other-olice. It is possible, therefore, where both centralloiiices'fhave access 4to the same group 'off-trunks, for two markers, one in each central office, to Vmake connection.simultaneously to the `:respective vframes havingA access to the same Ivgroupof trunks, 'If rthis association occurs at lthe. sameltime, andifboth markers test the same -trunkin a group atiaboutthe `same instant, it is possible `that both of 4them may simultaneously ,seizefthettrunk neither marker rrecognizing the .xfactithat the other one is also testingand seizing .the desired trunk.

The 'disadvantage abovementioned may be 'overcome yaccording Vto a feature of the rpresent r-inventionfbyarranging,the group of markers yof one .central ',oiiicepunit iso-,make a double test .,lofzthertrunks.immediately following their initial y nsartest and Aseizure thereofrandby arranging .the

1938, Serial No. 214,355

group of markers of the other central oiiice unit to make a double test of the trunks after a substantial interval of time has elapsed following the initial test and seizure. Any one of the markers of either kgroup on seizing the trunk following the initial testimmediately applies a busy condition thereto, and a marker of the iirst group on making its double -test immediately following its seizure williind the trunk busy in the event that a marker of the second group made a simultaneous initialftest and yseizureof the same trunk.

The markers of the vfirst group are so arranged that they will release the ,trunk if ythey find it idle on the vsecond test and .willproceed .to bring yabout a second trial to extend the Iconnectionfleaving thetrunk to the use 4of the marker in the second group. When, therefore, the marker in the Ysec- .ond 'group subsequently performs its double test of the trunk, Ait `ywill find the Atrunk clear, since the marker in therst group has Ialready performed c its double -testand has `released `the trunk. Should the rnarllzer inthe ,first group complete its double test before the-marker in the second group .applies the busy condition tothe trunk, or, should the rmarker in the first group fail .todetect the `busy A `condition applied by `the marker of the second group, the first marker .would assume ,that the trunk was free and Iwould proceed tov establish the connection -over it. When, therefore, the second marker performs its .double Itest at a later time, it inds thetrunk busy by reason of its seizure bythe ,marker in the firstgroup, and `the `second ,marker thereupon withdraws and rbrings Yabouca second .trial-for the call .with vwhich it is dealing.

The foregoing and other features of the invention will vv:be described more fully in detail in the :following specification and will also be set forth inthe appended claims,

lReferring now to the drawings which accomy pany vthe specification, Figs. 2te '7,` inclusive, when .taken yin thel order shown in Fig. l, disclose schematically `the manner in which two central oflice units, in the same building but/independent exceptfor the fact that ythey makecommon use of certain-groups ofr outgoing trunks, `arepresender and the district and oice switches to originating markers.

Fig. 3 shows in more detail parts of a secondary cross-bar ofce switch, an oiiice link connected to the primary oice switch on Fig. 2, two out'- going trunks from the secondary office switch, and that part of the oilice frame connector which connects the test leads of the outgoing trunks to markers. I

Fig. 4 shows part of an originating marker.`

Figs. 5, 6 and 7 show the same equipment for another central oiiice unit in the same building,

yas Figs. 2, 3 land 4 respectively. The circuits are the same except the markers, which differ in this respect, that the one shown in Fig. `4 is arranged to test an outgoing trunk for a double vconnection immediately after selecting such a trunk for use, whereas the one shown in Fig. 7 tests the selected trunk for a double connection at a later stage in its operation.

Hereinafter the equipment shown in Figs. 2, 8 and 4 will be referred to as the irst central oice unit, and the equipment shown in Figs. 5, 6 and '7 as the second central oflice unit. The switches, switch controlling circuits, register senders, switch controlling markers and the various connectors which serve to interconnect these devices in the establishment of a telephone connection may be of the types disclosed and described in detail in the patent to Carpenter, No. 2,093,117 of September 14, 1937, and in Carpenter application Serial No. 214,356, filed June 17, 1938. Many of the details of the system illustrated in thepresent drawings have been omitted for the reason that they are not essential to a thorough understanding of the invention. These details, however, may be substantially the same as those fully disclosed in said Carpenter application, and reference may be had thereto for an understanding of them. The automatic switches illustrated in this invention are of the cross-bar type and may in general be the same as the one disclosed in the patent to Reynolds 2,021,329, granted November 19, 1935.

Assuming that a call is originated by the subscriber at station 200, whose line 20| terminates `on primary line switch 202 in the first central oiiice unit, a train of operations is started which selects an available path to an idle sender, and operates select and hold magnets on the primary and secondary line switches and sender link switches to close that path from the subscribers lineto the sender. This connection is shown through line link 203, secondary line switch 204, district junctor 205, primary sen-der link switch 206, sender link 201 and secondary sender link switch 208 to sender 209. District junctor 205 also terminates on primary district switch 2| I.

The subscriber dials the oilice code of the desired terminating office, and when the code is registered in the sender the latter causes itself to be connected by connector 2 I 0 to an idle originating marker, such as the one a part of which is shown in Fig. 4.

The oflice code is transmitted from the sender to the marker, resulting in the operation of offnormal relay 428 to supply certain operating and locking ground connections in lthe marker while it is engaged on this call, and of a certain route relay, such as relay 422. The operation of this particular route relay, among the numerous route relays of the marker, locates the group of outgoing trunks leading to the desired terminating to the secondary oice switches on all the omce Aboth central ofce units.

frames of the first central oilice unit. This 'loeating is done in two steps; rst by selecting a test group of forty trunks including perhaps groups to several destinations, and which 'are connected, one trunk to a level, to two certain levels on each of the ten secondary switches of each of a certain pair of oiice frames; and then by marking two trunks in the group of forty, one the 'rst and the other the last of a block of trunks which lead to the 'desired destination. For the purpose of determining the idle or busy state of each of the trunks of a test group of forty, the marker has forty trunk test relays, of which only four are shown, namely relays 4|0, 4H, 4l4 and 415. There are also forty relays, one of which will be operated to designate the trunk selected for use, and of these also only the four are shown which correspond with the four trunk test relays shown, namely, relays 4H, 418, 419 and 420. Upon the operation of relay 422, one of its contacts connects battery through conductor 432 and the winding of relay 304 to ground, operating that relay. Relay 304 is common to a pair of ofce frames and individual to the particular marker. The operating circuits of the similar relays for the several markers, associated with one pair of olice frames, are wired in a preference chain which is not shown, to prevent any two operating together, so that at any one time only one marker can deal with a particular pair of oice frames. By grounding conductors 308 and 309, relay 304 operates relay 305 for the office frame partly shown in Fig. 3, and a similar relay for the other frame of the pair, which may be called the mate frame, these relays also being individual to the particular marker. Another contact of relay 422 causes relay 400 to operate, this last being associated with the particular pair of levels on the twenty secondary office switches, ten per frame, to which the forty trunks of the test group are connected. The bottom contact of relay 400 connects ground through conductor 433, a contact of relay 305, conductor 3l0 and the windings of relays 306 and 301 in parallel to battery, operating relays 306 and 307, which are associated respectively with the two levels yin all the secondary switches. I'he top contact of relay 400 connects ground through conductor 434 to the mate frame, where it operates relays corresponding to 306 and 301.

Relays 305, 306, 301 and the corresponding ones in the mate frame connect the windings of the forty trrmk test relays to the test conductors of the forty trunks. Thus the winding of relay 4|0 is connected through break contact of relay 4H, conductor 455 and make contacts of relays 305 and 301 to conductor 3i l, which is the test conductor of outgoing trunk 300, connected to crosspoint 302 and multipled to nine or nineteen other cross-points in the same level of the same secondary ofce switch, and also multipled to crosspoint 602 and other cross-points in the same level ofthe corresponding switch in the second central oflice unit. The winding of relay 4l l is connected through break contact of relay M8, con` ductor 436 and make contacts of relays correspending to 305 and 30'! in the'mate frame to the test conductor of the next higher numbered trunk, which is connected to the same level of the corresponding switch in the mate frames in The windings of relays 414 and 4|5 are connected through similar circuits to the test conductors of two trunks conn nected to the nexty higher level in the same switch in bothfframes in both central oiice units, trunk aderito armature springsof relay 305 indicate multipling tofe'orrespondi-ng relays in the same frame but associatedV with other' markers. Those shown connected to ythe armature springs` of relays 306 and 301 ifndicatemultiplingto corresponding relaysin the' s'arne frame but associated with other levels to which are connected other test groups ef fortytrunks each.A If outgoing trunk 300 is busy ona connection previously established, it is madesoi by crosspioint-BGZ or one of the others oxr'tlie-sarne levelsin the'fsame' switch,` or cross- A poritBOZ orforie of tli'eothers' on the same level tir inE tlfleisaine- -skwitcl-"i, being closed. That grounds the testconduetor 3l|i and causestrunk test re-v lay 4`l0 t`ooperate7 it having. battery connected to the' other end of its winding. I-n the same way al1/ofthelvforty trunk-test relays which are con-I nee'ted tobusytrunks willA operate. v

' I-wov other'contaicts ofy the operated-route relay 4'22, -by grounding conductors 4311 and 438, block out of theforty trunks those whichv constitute the trunk group to the desired destination.

`This trunk grouplmay contain any even number of trunks from two to forty. There are twenty relays' similar to relays 400 and 4|3, and by con'-A necting conductor 431 to the winding of one of them and thereby causing it to operate when route relay 422'operates, the first trunk of the group-is marked. There are also twenty relays similar to relays 4I2and 4I6, and byv connectingy conductor 438 to the vwinding of one ofV them yan'dfthereby causing it `to operatewhen route relay 422 operates, the last trunk of the group lisy marked.r Connecting conductor 431 to relay 409,

. and conductor 438 to relay 416, as shown, identiiles` the rtrunk group as consisting of the four trunksfwhlch are now connected to the windings ofn the trunkv test relays 4| 0, 4| 4I4, andy 415,.. that is, the rst of the group is trunk 300; the second is the one corresponding to 300 in the mate frame, the thirdk is 30|, and the fourth and last is the one corresponding to 30| inl the mate frame;

The next stepzisto operate oneV of relays 411, 440, 4| Brand 420.to select for use the rst one of the four trunks which happens to be idle. Whenrelays 306, 301 and the corresponding relaysV inthe mate frame -have operatedl to connect the forty trunk test relays to the forty trunks, a

circuit is closed fromfground through make contacts ofrelays306`, 301 and 305, conductor 430` and.v the winding of relay 40| to battery, vand a y similar circuit'from the mate` frame over con- 'relay 420,- the low''r of relay 406, and r`els`tarice'405 tol battery. When relays 40| and 4t2E have tetrroperated; the direct `gmuml ponnectiorr to ythe uppr"winding ofv relayv406 is brolnrr,` but current continues through it for atithe; charging condenser 403. As the condenser cha-rges'- up this ycurrent dies down', until the lower wirdi-iig oyerpowers the upper and the relay opratesf.- rIhis slow operation allows time for the trunk test relays, such as relay lllll',` to operate'.l Relay 401 has beenoperated from the begiri-ning by a circuit from ground through make Contact of relay 428, break contacts of the forty trunk selecting relays including 4| 1 to- 420 inelusive", and winding of relay 401 to' battery. lf all four trunks of the group -are busy, relay 408 will olinerateI by a circuiti-rom ground through make contacts of relays 406',v 401, 409, 4"'lf0 and 414, break contact of relay 4I`2`, make contacts of relays 4|4, 4| 5' and 4|6, and the winding of relay 408" to battery. This will result in the marker abandoning the atternpt to'V corn-plete' the call over'this route,y and trying instead to complete it' over' an alternate route or to an overflow trunk. I however, the rst two trunks are busy and the third idle, with relay 414 normal, relay M9 wil-l: operate by the same circuit through the break contact of relay 4"'l2, andl thence tlir'ou'ghf break contact of relay 414 and thev winch ing! of- 4492y to battery. Relay 4|f'9 operating locks up through the back contact chain to its left, and at the s'ar'ne time breaks the back Contact cli-dihto its right, thereby releasing relay 401. This-Breaks the circuit which operated relay 419 andf' thereby prer'fent's the'y operation of any earlier relayA of the same kind, rsuch asl 4H or 418, in caseV an'r earlier trunk test relay such as 41'0 or '4H-'i should release upon its trunk becoming idle. Relay 45|@ operating' also'tra'Lnsters'v the connection O'f'tle test Conductor 312A of the idle ,and selected tr-k '301i from the winding of trunk test relay 4|`4f to2 ground through topmake contacts ol relay`s42lZ and? 429,thus immediately r'narkingv the trunk4 as' busy,` incase a marker of the second central office unit should test it. Relay 429` has been operated' from the beginning by a circuit froml ground through make'lcontact of relay' 428, break contacts; of relays 420, 425, 424 andA 423, and winding of 4-29t'o battery. Relay 42| operated froir1'-thefront contact of relay 429;

Relay H9l operating also causesrelay 425 to operate; thewlnding of the'latt'er being multiplied to tl'e'ground'ed bottom make contact ofrelay 4l9 and every fourth relay of the same kind to the left or right. Relay 425 operating causes relay 429toreleas'e, which breaks the operating circuitoff relay 421i If at this moment thereis any other` groundj connectiony to test conductor 312i relay' 42| will hold operated through its top make contacte although its operating circuit has been' broken` by the release ofv relay 429; Such a ground connection apparently clidy not exist when the forty trunks were tested, and it can exist*r nowVv only because `of-A interferenceV by a markerE of the second central ol'ce unit, or because the trunk wasbusy all the time and that factwas'not disclosed during the test of the forty trunks on account of some break in the wiring. Iitdoesexistv and relay 42 I` holds operated, relay 4`2-'lfvlii1l1 operate by' a circuit from 'ground through breakcontactof' relay 4'29` and make contact of relayA "421-3 This will cause the marker to send a' vsoc'f1; lleili trouble' release signaly to thev sender, resultingi the"v dismissal? of 7 the marker and the calli-ngi.otanothermarker for another trial.- Bar- -erations, or relay 423, 425, or 426 operating in case another outgoing trunk had been selected' would do the same, which if not blocked by a trouble release involves the operation of district and office frame connectors 2|4, 2| 5 and 2|6 to connect the marker to various parts of the district and oiiice switches; the testing of all possible paths from primary district switch 2|| to the secondary oiice switch to which is connected outgoing trunk 30|; the selection of an available path such as the one shown through district link 2| 1, secondary district switch 2|2, oflice junctor 2|8, primary oflice switch 2|3, and oiiice link 2|9; the operation of select and hold magnets in the primary and secondary district and oilce switches to close through this path, thus completing a connection from subscriber station 200 to outgoing trunk 30|; and the release of the marker from service on this call, all in the manner disclosed and described in said Carpenter Patent No. 2,093,117 of September 14, 1937.

Assume now that a call is originated by the subscriber at station 500, connected to the second central oflice unit, instead of by a subscriber connected to the first unit. The subscribers line being connected to a sender such as sender 509, through line switches 502 and 504 and through sender link' switches 506 and 508 and the sender to a marker such as the one shown in Fig. 7, through connector |0 all in the same manner as described above, that marker will proceed just as described above, testing the same forty outgoing trunks and may select for use the same trunk 30| by operating relay 1|9, which in turn operates relay 125. Relay 125 starts a chain of operations culminating in the completion of a connection from the calling subscriber to outgoing trunk 30|, unless blocked by a trouble release, just as did relay 425 in the rst call described. In that call relay 425 operating also caused the release of relay 429 and thereby the breaking of the operating conductor to the winding of relay 42|, butV this marker has no relay corresponding to relay 429, and the operating lead to the winding of relay 12| which corresponds to relay 42| is not broken' at this time and so it does not now release under any conditions. In this marker the operating-conductor to the winding of relay 12| 1 is wired to ground through a make contact of relay 132, which has been operated from the beginning through a chain of break contacts on a set of relays represented by relays '|30 Aand 13|. Relays 130, 13| and 132 have their counterparts in the. marker shown in Fig- 4, serving the same principal function of selecting a path, but they are not shown thererbecause they have no function withregard to releasing relay 42 I.

Among the chain of operations following the operation of relay 125 are those involving the testv of allpossible paths from the primary district switch to thesecondary office switch and theselectionfof an available path. This results in the operation of one of the set of relays represented by relays 130 and 13|, that marking the selection of a particular path. The operation of this relay-causes relay 132 to release, and that breaks the operating conductor to the Winding of relay 12|. As described in the case of relay 42| in the l other marker, relay k12| willrelease and permit the marker to proceed to a successful completiony Vcan exist only because of interference by a marker of the lrst centraloiiice unit, or because the trunk was busy all the time and a trouble condition prevented that fact from appearing when the forty trunks were tested. If relay 12| does not release, relay 121 will operate and causea trouble release signal as described in the case of the other marker, and with the same results.

Now suppose that the subscribers at stations 200 and 500 originate calls for the same terminating oflice at the same time. The two markers will function independently and without possibility of mutual interference up to the time that they both test the group of forty trunks. If either marker arrives at this stage much before the other, it will select an outgoing trunk such as trunk 30 I, operate its relay 4| 9 or 1|9 as the case may be, and thereby ground test lead 3|2 and so operate relay 1|4 or 4|4 in the other marker, which will cause that marker to pass over trunk 30| and select a higher numbered trunk. But if both markers coincide very closely in time of testing the forty trunks, relays 4|9 and 1|9 may both operate and lock up, meaning that both markers have selected the saine trunk 30|, and resulting in their both connecting ground to the test conductor 3|2.

What will usually occur in this event is that the rst or Fig. 4 marker, making an immediate attempt toI release relay 42| by releasing relay 429, will fail to do so because the second or Fig. 7 marker, making no such attempt at this time, continues to hold a ground connection on test conductor 3 2. The iirst marker will send a trouble release signal and will be dismissed, breaking its hold on the test conductor, before the second marker is ready to attempt toy release relay 12| by releasing relay 132. When the second marker does make that attempt, it will nd the test conductor clear and will proceed to establish a connection to the trunk.

Possibly it may occur that relay 42| will release before the test conductor is grounded by the operation of relay 1|9.A In such a case the first marker will establish a connection lto the trunk, and the second marker, when it attempts to release relay 12|, will fail to do so and send a trouble release signal.

What is claimed is:

1. In a telephone system, a. group of trunks, two markers having simultaneous access to said group, each marker provided with means for testing the trunks and for selecting an idle one for use, means in one of said markers effective upon selection of a trunk for making a test to determine. if another marker has selected the same trunk, means in a second one of said markers effective after an interval following the selection 4of a trunk by said second marker for making a test to determine if another marker has selected the same trunk, and means in the marker that is first to perform the said test for causing it to release the trunk which it has selected if the test indicates that another marker has selected the same trunk.

2.l In a telephone system, a group of trunks., two markers having simultaneous access to said group, each marker provided with means for testing the trunks and for seizing an idle one thereof for use, means in each of said markers for Aappl-ying a busy condition to a trunk as soon i test of said trunk to determine if another marker has seized the same trunk, means in the second one of said markers effective after an interval hasexpired following its testing and seizure of f a trunk for making a second test of the trunk to determine if another marker has seized the same trunk, and means in each one of said markers effective to cause it to Vrelease a trunk when it finds the same busy as a result of the second test thereof.

3. Thev combinationin a telephone system of a group of'r conversational circuits, a first testing mechanism anda second testing mechanism hav- I1; ing simultaneous access to said group of circuits, ,bothkof said mechanisms provided with means for testing the circuits and for seizing` an idle 'one thereof for use, means in each of said mechanisms effective when said mechanism seizes an idle circuit to apply ka busy condition to said seized circuit, means in the first one of said Y mechanisms for removing the busy condition it has applied to a seized circuit following the seizure thereof and for making a second test of said circuit to determine whether it has been seized by another mechanism, means in said firstmentioned mechanism for causing the same to release a seized circuit if it finds the circuit busy on said second test, and means in said second mechanism effective after an interval of time has elapsed following the seizure of a circuit for removing the busy condition applied to the seized circuit by said second mechanism and for performing a second test of said circuit to determine whether it has been seized by another mechanism.

4. The combination in a telephone system of a group of trunks,'a first group of markers, any one of which may have access kto said group of trunks, a second group 'of markers, any one of which may have access to said group of trunks simultaneously with any one of the markers of said first group, means in each of said markers Vfor testing and seizing any one of the trunks in said group, means in each one of the markers of said first group effective upon the selection of a trunk by one of such markers for making a second test to determine if a marker of said second group has selected the same trunk, means in each of the markers of the second groupv effec'- tive after an interval of time has expired followingthe seizure of a trunk by one of said second vmarkers for vmaking a second test of the trunk to determine if it has been selected by a marker of the first group, and means in each one of said markers effective to cause such marker to release a trunk that it has seized if it finds the trunk busy on performing the second test thereof.

5. The combination in a telephone system of a group of trunks, a train of automatic switches for extending a connection to said trunks, a second train of automatic switches for extending a connection to said trunks, a first marker and a second marker, both of which have access simultaneously to said group of trunks, means in said markers for testing said trunks and for seizing an idle onev thereof for use, means inv said first marker for making a second test of a seized 'trunk to determine whether the trunk has been seized by said second marker, means in said first marker for releasing the trunk if it is found busy on said second test and for proceeding to prepare the switches of said first train for operation if said trunk is found idle on said second test, means in said second marker effective after it hastested and seized an idle trunk for preparing the switches of said second train for operation, means in said second marker effective after it has prepared said switches for performing a second test of the trunk seized by said second marker to determine whether said trunk has been seized by said first marker, and means in said second marker for causing it to release the trunk if it finds the trunk busy on said second test and for causing said second marker to proceed with the establishment of' a connection if it finds the trunk idle on said second test.

RAYMOND E. COLLIS. JAIVIES B. NEWSOM. 

